As-synthesized single-walled carbon nanotubes (SWNTs) contain mixtures of metallic and semiconducting species with different diameters and chiral angles. Semiconducting SWNTs are known to exhibit superior field-effect behavior. To minimize the effect of tube-to-tube variation on device electronic properties, networks of SWNTs, rather than individual nanotubes, have been applied in producing field effect transistors (FETs). FETs employing SWNT networks (SWNTnets) in the active channels are quite reproducible and printable, making low-cost macro-electronics possible. SWNTnet-based FETs have achieved mobilities higher than those typically achieved with semiconducting polymers. However, the presence of metallic tubes in SWNTnets impairs or destroys the switching behavior of semiconducting tubes. There exist numerous approaches to separate semiconducting SWNTs from metallic SWNTs. These strategies include the synthetic strategy of selective growth, post-synthesis solution-based separation methods (such as electrophoretic separation, dielectrophoresis, chromatography, density gradient ultracentrifugation (DGU), gel-based separation techniques, selective aromatic extraction, surfactant extraction, amine extraction, surface alignment and selective polymer wrapping) and fabrication-based techniques such as electrical breakdown of metallic nanotubes. However, many of the proposed methods do not achieve full semiconductor device yield, or do involve substantial costs.
Selective functionalizations of SWNTs using small aromatic molecules which can strongly interact with SWNTs via π-π stacking interaction, have been used for selective separation of SWNTs. Such molecules include diazonium salts, pyrene derivatives, porphyrine derivatives, pentacene derivatives and flavin mononucleotide. However, most separation techniques are still insufficient to remove metallic SWNTs to an extent sufficient to meet the requirements for electronic devices.
Thus it is an object of the present invention to provide alternative methods for enriching specific species of SWNTs.